Silicon wafers are the building blocks of a wide variety of semiconductor devices, such as solar cells, integrated circuits, and MEMS devices. For example, Evergreen Solar, Inc. of Marlboro, Mass. forms solar cells from silicon wafers fabricated by means of the well-known “ribbon pulling” technique.
The ribbon pulling technique uses proven processes for producing high quality silicon crystals. Such processes, however, may produce ribbon crystals having relatively thin areas that are prone to breaking. For example, FIG. 1 schematically shows a cross-sectional view of a part of a prior art ribbon crystal 10A. This cross-sectional view shows a so-called “neck region 12” that is thin relative to the thickness of the rest of the ribbon crystal 12.
To avoid this problem, conventional ribbon pulling furnaces may have meniscus shapers for varying the shape and height of the interface between the growing ribbon crystal and the molten silicon, thus eliminating the neck region 12. Although beneficial for this problem, meniscus shapers necessarily must be cleaned at regular intervals to ensure appropriate furnace operation. Consequently, the entire crystal growth process must be suspended to clean the meniscus shapers, thus reducing yield. Moreover, meniscus shaper cleaning requires manual/operator intervention, thus driving up production costs.